Prismatic reflector



Oct. 3, 1939. T, w RQLPH 2,175,067

PRI SMATI C REFLECTOR Filed April 23, 1938 //////jml\\\\\\ T 1 Thomas W Ralph ATTO R N EY reflecting prisms of substantially 90.

I Patented Oct. 3,1939

.sTA'rE-sf 2,175,067 I I PRISMATIC REFLECTOR Thomas W. Rolph, Newark, Ohio, assignor to Holophane Company, Inc., New York, N. Y., a orporation of Delaware Application April 23, 1938,?Serial No. 203,744

7 Claims.

These objects are accomplished by utilizing prisms in pairs and shaping each prism so that the light is reflected from one prism across the intervening space between the two prisms and after enteringthe second prism is reflected back in the general direction from which it came.

The outer surface of the average prismatic reflector is provided with a plurality of double The interior face is generally smooth. .The new form of prism described herein uses two faces which are curved and which form an angle substantially less than with each other.

The accompanying drawing shows, for purposes of illustrating the present invention two of the many embodiments in which the invention may take form, it being understood that the drawing is illustrative of the invention rather than limiting the same. I i In the drawing; I

Figure 1 is across-section of a 90 double reflecting prism as employed on the surface of a prismatic reflector;

Figure 2 is a cross-section through several prisms of the new type as used on a prismatic reflector;

Figure 3 is a cross-section similar to Figure 2 indicating also the action uponincident light which is converging; v

Figure 4 illustrates, a typical prismatic reflector with these prisms running radially; and

. Figure 5 illustrates a prismatic reflector in which these reflecting, prisms are annular, the reflector being used within a shade.

Figure 1 shows in cross section atypical 90 double reflecting prism, as now foundin the art, the apexbeing at I and the valleys being at points 2-and 3. 44 represents the inner surface of the reflector on which this prism is placed. 5 represents a lightray entering the inner surface 4, reflected successively at the. two surfaces of the double reflecting prism and leaving the inner surface in a direction parallel to the direction of incidence. In this figure the light ray is shown as entering the surface at 'normal incidence. When a light ray enters the surface at angles slightly different from the normal, reflection still occurs at the two surfaces of the prisms,but when the angle of the entering ray is more than a few degrees (the amount depending upon the index 7 of refraction of the medium) away from the nor-,.

mal incidence, transmission occurs at one of the two reflecting surfaces. .This is illustrated by' rays 8 and I in Figure 1.

Figure-2 shows the action obtained'with the new form of prism. Light rays 8, 9 and I0 enter the smooth inner surface of the reflector H--ll normal to the surface and are reflected from the first. prism surface 12. They pass across to the second prism surface l3 and are: refracted at this surface in the direction of the next prism."

They enter the next prism I4 and are refracted at this surface into the proper direction for reflection from the second surface I5 of the second prism. This reflection directs them back'through the smooth inner. surface of the reflector in the general direction from which they came. Surfaces I3 and I4 are not refracting surfaces only. They also act as reflecting surfaces to cooperate with other adjacent prisms. For example, light ray. I6 enters the smooth inner surface of thereflector and is reflected from reflecting surface I4 across to prism surface I5 where it is refracted and enters the next adjacent prism at surface ll. Here it is refracted again and reflected from the opposite surface I8 of this prism and goes back in the general direction from which it came in the same manner as light rays 8, 9 and I0. Another light ray I9 is indicated using surface I3 as av reflecting surface and entering the adjacent prism on the other side.

It is clear, therefore, that each prism surface acts as a reflecting surface for some of the light rays and as a refracting surface for other light rays. By shaping the surfaces properly, this action can be controlled so that the maximum amount of light is reflected from the first prism and enters the second prism at angles insuring reflection from the opposite-surface of the-second prism. Note that the light rays entering the inher surface of the reflector .at normal incidence I and striking reflecting surface I2 at different points along the surface; all tend to converge at the center of the. second reflecting surface I5. This indicates that incident light which is not normal to the inner surface of the reflector can still be received and reflected by surface I5, as will now be described in connection'with Figure 3. Figure 3 shows the action of converging light rays received by these reflecting prisms as used on a prismatic reflector. the smooth inner surface 20--20'of the reflector in Figure 3 at-normal incidence. It is reflected Light ray 2| enters from the first surface 24 of the first prism, passes across into the second prism and is reflected out again in the same way as the light rays indicated in Figure 2. Light rays 22 and 23, however, do not strike the inner surface --20 at normal incidence. This may be due to the fact that the light source is of appreciable size and not all of the light comes from its exact center, or it may be due to other causes such as the light source being somewhat off-center in the reflector. Whatever the cause, it is desirable to deal with this light as efficiently as possible. Within a certain angle or spread, these light rays 22 and 23 are reflected from the first surface of the first prism, refracted at the second surface of this prism, enter the second prism and are reflected out as indicated. It will be seen that although these two light rays 22 and 23 do not enter the inner g which they came.

surface at normal incidence, they are nevertheless reflected back in the general direction from which they came and the reflector, therefore, handles them efiiciently.

These light rays 22 and 23 of Figure 3 correspond to light rays 6 and I in Figure 1. There is this important difference, however. It is found that in this new form of prism, light rays 22 and 23 may be spread farther from the central light ray and still follow the desired path through the prisms and be reflected back in the direction from In other words where light rays 6 and 1 in Figure l emerge from the reflector on the outside of the prism, light rays 22 and 23 of Figure 3 do not emerge on the outside of the reflector but emerge on the inside, having been reflected into the desired direction. This results in an increase in the spread of light which can be handled efliciently by a prismatic reflector. In this lies a great advantage of these new prisms. They increase the amount of light which can bereflected from a prismatic reflector as used with the customary forms of light sources.

When the spread of incident light is too great, however, some of this light will be transmitted. Such a light ray is indicated at 26 of Figure 3. This light ray striking the inner surface 202ll at a considerable angle from the normal ray 2| is slightly refracted and passes to the first surface 24 of the first prism. Here itis reflected and goes on to the second surface 25 of the first prism. Here light ray 26 is transmitted and refracted in the same way as the otherlight rays, but due to its direction, light ray 26v is refracted at an emerging angle which misses the second prism. While it misses the second prism, it passes out in directions close to the second prism. Hence it emerges in directions nearly tangent to the general contour of the reflector. This is sometimes a decided advantage as will be pointed out below in connection with Figure 5.

Figure 4 shows a prismatic reflector 26' of the usual form having radial reflecting prisms. Such a reflector is suitable for this new form of prism. The prisms can be placed on the reflector in the same way that customary reflecting prisms are used and an increase in efllciency will be oh- 1 tained.

Figure 5 indicates a case in which it is advantageous to use the prisms running horizontally around the reflector. This shows a lamp 3 surrounded by a light-director 21. This light-director 21 has a lower portion 28 which is refracting to give a wide spread of light outward and downward. The upper portion 29 is approximately spherical in contour and carries reflecting prisms to reflect the light back toward the refracting portion 28. These reflecting prisms are placed horizontally and are of the form described herein. A light ray 30, for example, leaves the lamp, strikes these reflecting prisms, passes from one prism to another and back in the direction from which it came. This takes it back through the light-source to be handled by the refracting portion 28 in the same way that direct light is handled.

As this globe or light-director is used for portable lamps, it is surrounded by a dense translucent shade 3|. This shields the eyes from direct view of the light-director. The light which is transmitted by the reflecting prisms will emerge in directions nearly tangent to the reflecting contour as shown in connectionwith Figure 3. Such transmitted light is-indicated in Figure 5 by light rays 32 and 33. Light ray 32 is typical of the light emerging in a generally upward direction and passing out through the opening in the top of the shade. Light ray 33 is typical of the light emerging in a generally downward direction and passing out through the lower opening in the shade. surface of the light-director in directions nearly tangent to its contour and such light generally misses the shade and passes out either in downward directions to be directly useful or in directions toward the ceiling to add to the general diffusion of light in the room. With the ordinary form of reflecting prism as indicated in Figure 1 this would not occur because much of the light which is not reflected would be transmitted in directions to strike the shade 3|.

If the prisms on the reflecting section 29 of the light-director were run vertically, they would still act efliciently as reflectors but the transmitted light would emerge in directions to strike the shade v3|. In this light-director, best efliciency is obtained by using prisms of the new form running horizontally on the reflecting portion.

It is obvious that the invention may be embodied in many forms and constructions within the scope of the claims and I wish it to be understood that the particular forms shown are but a few of the many forms. Various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.

What is claimed is:

1. A prismatic reflector having its prisms ad- 'J'acentone another and separated by intervening air spaces, each prism having two curved faces concave toward each other, symmetrical with re- Thus the transmitted light leaves the spect to a central prism axis andintersecting at an apex, one face of each prism intercepting a light ray in the medium of the reflector generally parallel with the prism axis and reflecting it toward the opposite face of said prism, which refra'ctively transmits it across the air space between consecutive prismsfthe adjacent-prism having its externally convex rcfracting surface, onto which said my impinges, for deviating said ray toward the opposite surface of said adjacent prism. at such angles that said opposite surface will totally reflect it into a direction substantially parallel with the axis of the said adjacent prism.

2. A luminair comprising-a light source of substantial size, a prismatic reflector about the light source and having a series of external prisms with their axes converging toward the light source, each prism having a reflecting face adapted to receive convergent light from the source for redirecting such light across the prism and a refracting face for transmitting such redirected light outside the refractor in a divergent beam of greater angle than the original angle of convergence with the dominant portion of said divergent beam at angles subtended by the next prism of the series, the next prism in the series having a light condensing incident face for transmitting the light across said prism and a reflecting face for condensing it to substantially the original angle of convergence and returning it toward the source.

3. A luminair such as claimed in claim 2, wherein the reflector is of arcuate contour transversely of the prisms and light rays emerging from the tips of the prisms and emerging between the prisms at angles substantially greater than 90 with the prism axis are transmitted in directions generally parallel with the profile of the reflector.

4. A prismatic reflector having a series of prisms adjacent one another and separated by intervening air spaces, each face of each prism being a light reflecting face for light rays in the medium falling on said face at the angles effective for total reflection and reflecting said rays at such an angle as to direct them onto the opposite face of the prism for refractive transmission thereby across the air space toward the adjacent prism, each face of each prism being adapted to receive light transmitted as aforesaid and refract it'toward the opposite face of the same prism for reflection thereby into a direction substantially parallel with that of the original ray.

5. In combination two adjacent prisms with faces at less than to the prism axis, the prism axes being substantially parallel, the remote faces of the prisms being at such angle to the prism axes as to totally reflect light rays parallel, or approximately parallel, with the axes and incident thereon, the adjacent faces of adjacent prisms being refractors for the said reflected rays and placing them on the said remote faces at such angles thereto as to be totally reflected thereby into directions substantially parallel with the direction of the original rays.'

6. In combination two adjacent prisms with outwardly convex faces at less than 45 to the prism axis, the prism axes being substantially parallel, the remote faces of the prisms being at such angle to the prism axes as to totally reflect light rays parallel, or approximately parallel, with the axes and incident thereon, the adjacent faces of adjacent prisms being refractors for the said reflected rays and placing them on the said remote faces at such angles thereto as to be totally re-- flected thereby into directions substantially parallel with the direction of the original rays.

7. A prismatic reflector having two internal light reflecting surfaces and two light refracting surfaces the four surfaces being juxtaposed to form two adjacent ribs and effect a reversal of the general direction of a light ray originating in a direction at which the first reflecting surface on which it falls acts to totally reflect the ray.

THOMAS W. ROLPH. 

